If port 20 is available, then an attacker can assume that FTP is being used.

Name: If port 20 is available, then an attacker can assume that FTP is being used.
Brand: Quizplus
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Quizplus · Accepted Answer

Port 20 is the default data transfer port for FTP, so if it is open, it is a good indication that FTP is being used. However, it is possible for FTP to use a different port for data transfer, so it is not a definitive indicator.

If Port 20 Is Available, Then an Attacker Can Assume